STM32L476 USB Hardware for custom application

[Naveenkrishna_V]

Hi ST,

Using the STM32L476 for a custom battery-operated application, on trying to implement the USB 2.0 through a type C receptable, I need clarity on the connections of the USB.

AFAIK the VBUS sensing on PA9 should be connected through a resistor divider to reduce the voltage to a safe level when the MCU is not powered. My doubts are
1. Can I power the MCU from the VBUS using the VDDUSB (only USB peripheral working is needed) or should I connect both the VDD and VDDUSB so that the MCU should be powered ON and the USB peripheral won't work with only the VDDUSB connected to the VBUS.

2. How much does the USB peripheral and the MCU both consume during startup considering VBUS can only supply 500mA.

3. Can VBUS be 3.3V or will it be only 5V

4. Recommended Specs for voltage regulator if VBUS is 5V

[TDK · Accepted solution]

1. Yes, VDD needs power as well as VDDUSB. You can use a 3.3V LDO to convert USB power to 3.3V to feed the chip. This is common.

2. Generally, chips consume tens of mA. Certainly well under 500 mA.

3. VBUS is always 5V to start.

4. Literally there are thousands of them and any will work. LDLN030 will work.

If you are designing a board, see the hardware design guide:

dm00125306-getting-started-with-stm32l4-series-and-stm32l4-series-hardware-development-stmicroelectronics.pdf

You can also post your finished schematic here for review if you want.

[Naveenkrishna_V]

Hi TDK, Thankyou for clarifying my doubts, I was designing a Battery Management System using the STM32L476 and have attached the schematics for the same. Can you please review these and let me know your valuable feedbacks.

[TDK]

I only looked at the STM32-portion.

• BOOT0 should be tied low directly or with a pull-down resistor. It should not be left floating.

That's the only issue I see.

I'm not a fan of having separate grounds and tying them with 0R resistors, but it should work.

[Naveenkrishna_V]

Thankyou for spending time looking at my schematics and correcting me.